1. Field of the Invention
The present invention relates to a thermal recording medium in which a local region of a recording layer is heated to a predetermined temperature to change the state of the local region (this operation will be referred to as a heat mode hereinafter) so that information is recorded or erased and, more particularly, to an optical recording medium capable of recording information by irradiation of a light beam and a method of recording information thereon.
2. Related Background Art
Various media have been proposed as thermal recording media capable of recording information in the heat mode. In particular, an optical recording medium capable of performing optical detection to record information as a change in the optical state of the medium upon laser beam irradiation and heating can record information at a high density. This optical recording medium is used as an optical disk or card in practice.
A change in optical state on an optical recording medium is exemplified in the forms of a recessed pit, the presence/absence or deformation of a reflecting film, a change in refractive index, magnetic reversal, and the like. Among them all, magnetic reversal is detected as a change in the polarized state of reflected light. In another form, a change in the optical state is detected as a change in amount of reflected light or the like.
In recording information on an optical recording medium and reproducing it from the medium, marks formed by changes in optical states are formed and recorded as a mark train corresponding to information, and this mark train is read time-serially by a predetermined operation, thereby reproducing the information.
In this recording of the heat mode, the size and shape of a mark to be formed are determined by a temperature distribution induced on a recording film upon local heating. The temperature distribution induced on the recording film is influenced by thermal diffusion in the planar direction of the film. For this reason, even if a heating region is shifted at a constant linear speed while the incident energy per unit time is kept constant, the temperature distribution to be formed changes in a complicated fashion, depending on the moving distance (length of a mark) and the distance from an immediately preceding heated region. FIG. 1 is a view showing the relationship between the input signal and the marks in a conventional recording technique. As shown in FIG. 1, when a recording layer is simply heated in correspondence with information in the conventional recording technique, the widths (vertical dimensions in FIG. 1, d&gt;a&gt;b&gt;c) of the formed marks vary depending on the information pattern. When such a mark train is read time-serially by light beam scanning, the mark read timings fluctuate depending on the mark pattern. As a result, original information may not be accurately reproduced.
To solve this problem, various recording compensation schemes for adjusting the incident energy per unit time, heating time, and the like in accordance with the information pattern are proposed. However, these recording compensation schemes undesirably complicate the recording means.